1. Field of the Invention
The present invention pertains to a method for determining the vapor pressure of a multi-component liquid, such as crude oil, using an eductor and associated equipment for determining the change in the slope of a curve which represents the change in the suction port pressure of the eductor as a function of the pressure differential across the eductor.
2. Background
Measurement of the vapor pressure of a multi-component liquid is difficult in that the various compositions of the liquid typically have different vapor pressures at a particular temperature. Conventional vapor pressure measurement techniques and systems perform operations to reduce the pressure acting on a sample of liquid in a controlled environment until the pressure remains substantially constant, indicating that the vapor pressure of the liquid has been reached. However, as certain components of a multi-component fluid vaporize, the vapor pressure of the remaining liquid changes to a different value. This phenomenon complicates conventional vapor pressure measurement techniques and results in inaccurate determinations of the true vapor pressure of a particular liquid composition.
The aforementioned deficiencies in conventional vapor pressure measurement techniques may be of particular concern when attempting to measure the vapor pressure of liquids such as crude petroleum which have various hydrocarbon compositions mixed therein. The handling and transport of such a liquid should usually be controlled to prevent unwanted vaporization of the lower molecular weight liquids during the transport and storage processes.
One relatively uncomplicated device for measuring vapor pressure of a liquid utilizes an eductor. Conventional eductor-type vapor pressure measurement devices operate to provide a liquid flow rate through the eductor such that a relatively large pressure drop across the eductor is assured whereby measurement of the flow stream pressure at the so-called suction port of the eductor provides for measurement of a vapor pressure condition of at least one component of a multi-component liquid. However, use of an eductor type system may not be accurate if the liquid to be measured is made up of various liquid compositions if only one flow condition is observed or if the pressure measurements are taken under the wrong range of flow conditions. The present invention provides a method and system for overcoming the deficiencies of conventional prior art vapor pressure measurement systems, particularly of the type utilizing so-called eductor devices.